The invention is related to a bearing unit, comprising a rolling element bearing having an inner ring means and an outer ring means, said inner ring means being fitted on an axle stub between two opposite mounting faces, means being provided for preventing fretting corrosion between at least one of said mounting faces and the inner ring means.
A railway axlebox bearing unit of this type is known from JP-A-972344. Said unit has an interposed layer between the shoulder and the backup ring, which is less hard than the material of said parts. The interposed layer aims at reducing fretting corrosion, which would normally occur as a result of the fluctuating loads in the train bearing unit while in service.
The layer in question may be adhered or plated onto the backup ring. This entails the manufacturing of a special backup ring, which limits the flexibility in use of such rings.
The object of the invention is to provide a fretting corrosion means for bearing units which is more versatile. This object is achieved in that at least one mounting face and the inner ring means engage each other by means of a non-metallic support ring, preferably a polymer support ring.
The non-metallic support ring according to the invention constitutes a separate engineering piece, which can be used in conjunction with standard parts of the train bearing unit in question, e.g. a standard backup ring.
The non-metallic support ring may be applied in several ways. Generally, the inner ring means is fitted between a shoulder of the stub and an end bracket bolted onto said stub, said inner ring means engaging the shoulder by means of a backup ring. According to the invention, the backup ring engages the inner ring means by means of a non-metallic support ring.
Furthermore, the inner ring means may engage the end bracket directly by means of a non-metallic support ring.
Also, the inner ring means may engage the end bracket indirectly by means of a pressure ring, said pressure ring engaging the inner ring means by means of a non-metallic support ring.
The bearing unit in may be provided with inner ring means which comprise two inner rings enclosing a spacer ring, in particular in the case of railway axlebox bearing units. According to a further possibility, said spacer ring may engage at least one of the inner rings by means of a non-metallic support ring.
As the support ring is a separate piece, it may fulfil additional functions. For instance, the support ring may comprise a labyrinth ring part so as to form a labyrinth seal in conjunction with a further labyrinth seal part connected to the outer ring.
The support ring may be given any desired shape so as to provide the required sealing function. Also, a soft rubber sealing lip may be moulded onto the labyrinth seal for providing full tightness of the internal bearing space.
Furthermore, the support ring may comprise sensor means for sensing the bearing rotation. Said sensor may be applied e.g. for monitoring of the axle in question, such as temperature, vibrations, or number of revolutions.
Additionally, the support ring may be applied for providing a grease reservoir, so as to ensure long-term lubrication of the train bearing unit.
The support ring may be fixed in several ways, and may be premounted e.g. by clamping. In this respect, the support ring and the inner ring means engage each other by means of a groove-rib connection.
Furthermore, the support ring may be connected to a backup ring or to a pressure ring. Also, the support ring may be connected to a spacer ring.
The support ring may be connected in several ways. Preferably, the support ring comprises an axial extension, which engages a recess in the inner ring or in the backup ring.
The recess may comprise an undercut groove, and the axial extension may comprise a tongue which is snapped into the undercut groove.
Furthermore, the support ring may have a tubular extension accommodated in a recess of the inner ring means.
The bearing unit according to the invention is particularly suitable for a railway axlebox bearing unit. In such application, the area between the railway wheel and the wheel box is critically loaded. In service, bending and radial displacements occur, which lead to corresponding bending and radial movements between the inner bearing ring and the railway wheel, resulting in an orbital movement.
Moreover, fretting-induced corrosion may occur in this area.
According to the invention, these adverse effects are avoided by means of the non-metallic support ring, in particular a polymer support ring.
The bearing may be a double row cylinder or a double row taper rolling bearing. Also, a ball bearing may be applied.